Disc brake system with ABS

ABSTRACT

An ABS brake system employs two axially slidable brake discs and four brake pads that are biased to have floating light random contact therebetween in the off brake position. The ABS controller operates the brake pads with about one half of the usual brake pressure and about double the number of the usual braking and release cycles. The floating axially slidable brake discs and four brake pads have reduced residual torque drag during the brake release cycle and have reduced hystersis. The result is operation at a higher frequency and with less amplitude, than the usual sliding caliper and fixed brake system, and a resolution of a modulating scale for cycling that is usually associated with a much lower coefficient of friction surface than is actually present.

This is a continuation, of prior application Ser. No. 09/335,304, nowU.S. Pat. No. 6,244,391 filed Jun. 17, 1999, which is a CIP of U.S. Ser.No. 09/303,183, now U.S. Pat. No. 6,247,560 filed Apr. 30, 1999, whichis hereby incorporated herein by reference in its entirety. which is aCIP of PCT/GB97/03388 filed Dec. 8, 1997, which is a CIP ofPCT/GB97/03386 filed Dec. 8, 1997.

FIELD OF THE INVENTION

This invention relates to an ABS braking system for motor vehicles.

BACKGROUND OF THE INVENTION

Typically, production vehicles, such as automobiles having a AutomaticBraking System (ABS) employ a single brake disc fixed to the wheel huband a sliding brake caliper mounted on a suspension member of thevehicle. Operation of a brake foot pedal by the operator with excessiveforce is sensed by a sensor, and a deceleration of the wheel is sensedby a wheel position or speed sensor mounted adjacent the wheel. Thewheel speed sensor particularly monitors for front wheel locking upwhile in the braking condition with its loss of steerability and itslonger stopping distance. The stopping distance of the vehicle may bemade shorter if the wheels are operated iteratively at a low slip ratherthan a longer, fully locked or skid condition. The brake caliper ispreferably operated at a high brake torque “apply” rate to increasebrake torque for quick response. Additionally, caliper preferably isoperated at a “high release” rate to decrease brake torque for quickresponse when the condition of lock-up is sensed as about to begin toallow the wheel to accelerate to a velocity approaching the vehiclevelocity.

In conventional production vehicles having this fixed brake disc andslidable brake caliper, a hydraulic piston in a hydraulic cylinder onthe caliper is operated to shift an inner movable brake pad into brakingengagement with one side of the brake disc fixed to a rotating wheel hubmounted on the vehicle suspension. A reaction force from the hydraulicfluid moving the piston shifts the slidable caliper to slide the caliperand a second brake pad on the distal end of a caliper into engagementwith the other side of the fixed brake disc. Typically, the brakingsystem operates with hydraulic fluid at a pressure of about 70 BAR ormore to provide the clamping pressure to opposite sides of the brakedisc.

From the foregoing, it will be understood that when high excessive forceis applied to a brake pedal by a vehicle operator causing rapidlydeceleration of the wheel towards the lock-up condition, the ABS sensorsand control system senses the rotational position of the wheel relativeto the vehicle's speed; and if these conditions are within preset storedparameters, the ABS hydraulic system is activated to operate the brakes.The ABS hydraulic system isolates the pedal-operated hydraulics, and thebraking operation is taken over by the ABS system, which causes thebraking effort to drop and allows the wheel rotation to accelerate orspin up. When the wheel spin-up approaches the vehicle speed, as sensedby the wheel sensor, but does not equal the vehicle speed, the ABShydraulics apply increased hydraulic pressure to the sliding caliper todecrease or spin down the braked wheel's rotational velocity. When thevehicle wheel spins down to approach vehicle lock as sensed by the wheelsensor and within the preset parameters, the ABS hydraulic pressure atthe slidable caliper is increased to allow wheel spin up. This processis iterated to provide modulation of the ABS hydraulic pressure and adeceleration of the vehicle's velocity to provide a stopping of thevehicle within a predetermined distance depending on the kind of surfaceon which the wheels are engaging. Manifestly, the stopping distance onice or other low coefficient of friction surfaces is greater than thesloping distance for higher coefficient of friction surfaces.Governmental regulations in many countries require the ABS brakingsystem to stop the vehicle within a set stopping distance for a givencoefficient of friction surface.

The ABS system senses the initial apply rate and release rates andscales or calibrates the resolution of subsequent “apply” and “release”rates to stop the vehicle. For example, the amplitude of the initialapply and release rates is quite high when the wheel is on a dryconcrete surface and the frequency of the brake applications andreleases is quite large in amplitude and at a low frequency. The ABSsystem then compares the frequency and amplitude of brake apply andbrake release rates relative to the preset stored parameters in acontroller and then operates the braking system according to thisalgorithm that is used to decelerate the vehicle's speed to stop thevehicle with the governmental stopping distance. This deceleration isusually a constant deceleration and is linear with respect to time andvehicle velocity or distance traveled. Hereinafter, this will be calleda vehicle deceleration curve, which need not be linear, but which isusually a linear curve. A graphical representation of vehicle wheelspeed and of hydraulic pressure shows that they are modulated along thistheoretical vehicle deceleration curve until the vehicle is slowed downto a very low speed, e.g., under 10 mph when the brakes are allowed tolock up to complete the stopping of the vehicle. If the same vehicletraveling at the same speed and braked with the same brake pedalpressure was traveling on polished ice, having a very low coefficient offriction, relative to the coefficient of friction for the concretesurface, the initial braking by the ABS system recognizes this and setsthe scale or calibration to generate a finer resolution with a morefrequent application and release of the brakes and with a smalleramplitude of wheel acceleration and deceleration. Thus, with a smallercoefficient of friction surface, the average pressure variation andwheel acceleration is less over the stopping distance.

Current ABS braking systems suffer from being relatively heavy inweight, in being relatively costly, and from operational deficienciessuch as operating at high pressures, high residual torque drag, andlarge hystersis losses. The present invention is directed to providing asignificant weight reduction, for example, with respect to onecommercial automobile, to reduce the weight of the braking system fromabout 18 kilograms to 15 kilograms of unsprung weight at the wheel. Acost saving of thirty (30%) percent or more can be achieved relative tothe braking system currently used on a commercial vehicle. As will beexplained in detail hereinafter, better operation is achieved with areduction in residual torque drag, which occurs when the brake pads rubagainst the brake disc when the brake pedal has not been operated. Areduction in residual torque drag results in a significant increase inbrake pad life, lower operating temperatures, and faster wheelacceleration as will be described in more detail hereinafter.

To facilitate acceptance and adoption of the braking system of thisinvention by original equipment manufacturers, the preferred brakingsystem of this invention may be used with the same installed ABScontroller and operating system on vehicles now in use. The preferredbraking system without the ABS control system is more fully described inthe aforesaid co-pending United States patent application and to alesser extent hereinafter in this application. This braking systemincludes twin slidable brake discs and four brake pads for rubbing orclamping engagement with the four sides on the twin brake discs and afixed caliper mounted on a suspension stub axle or knuckle. Preferably,the hydraulic cylinder for operating the brake discs is formedintegrally with the suspension knuckle; and an outer, distal brake padis fixedly mounted on a stationary bridge of the caliper. This is unlikethe current slidable caliper on the typical conventional disc brake thathas only two rubbing surfaces engaging opposite sides of a cast iron orcast aluminum, heavy brake rotor.

The present invention is, as stated above, directed to providing abetter ABS system from an operational standpoint. Current ABS systemssuffer from a number of shortcomings. One of these shortcomings is thatthey operate at relatively high hydraulic pressures, for example, 70 BARon high friction surfaces. With only two braking surfaces for a wheel, alarge amount of energy must be dissipated at each rubbing surface todecelerate the vehicle quickly. These high brake pressures result inlarge amplitude variations in hydraulic pressure when the brakes arebeing applied and released, During the long period of time that thebrake pressure is released to allow wheel acceleration toward thevehicle's velocity, the vehicle is moving forwardly with no brakingeffort being applied to decelerate the vehicle.

With a finer resolution of the frequency and amplitude about atheoretical, vehicle braking curve, the time for an individual cycle ofbrake application and brake release is much quicker so that many more ofthese cycles are performed in the same period of time than for higherresolution braking system. Hence, it would be desirable to have an ABSsystem with increased resolution ore closely approximating the vehicle'sdeceleration curve. Another factor involved in the obtaining of betterbraking and, also in obtaining finer resolution of braking and releasingcycles is that of the hystersis of the system, which involves wastedenergy and time put into the system. For example, in the currenthydraulic systems there are expandable, flexible, hydraulic hoses orlines that expand during the high pressure braking and contract duringthe lower pressure release of the brakes. Also, several seals areexpanded during high pressure braking and then contract during thepressure release. One such seal in a hydraulic braking system is theannular seal about the piston of the brake caliper's cylinder. This sealis expanded during braking and contracts during brake release and exertsa return force to return the piston.

Another operational shortcoming of the commonly used slidable caliper,single disc braking system is the amount of deflection of the distalbrake pad's support at an outer end of the caliper. That is, in thecurrent disc braking system, the large, heavy sliding caliper has afixed pad on the caliper which is that outer end of a caliper bridge.This caliper and its bridge are large and heavy because they carry thepiston and the outer distal pad and provide the stiffness needed toresist bending and deflection from the large clamping forces beingapplied. Despite its being relatively heavy and large, the caliper'sdistal end often deflects about 0.0006 inch or greater. The operation inthe system is affected by this deflection of the caliper's distal endand the time needed to slide the heavy caliper back to its brake releaseposition.

As stated above, the operational performance of an ABS disc brake systemis adversely affected by residual drag of the brakes when the brakingpressure has been released. Residual braking torque retards wheel spinup to the desired speed, and thus, slows the time of response. It hasbeen found that the conventional slidable caliper brake disc hereindescribed has significant residual torque or brake drag. One cause maybe that the brake disc is fixed to a stub and whatever tolerance it hasfrom a true perpendicular relationship to the rotational axes of thewheel results in rubbing of the disc at high spots, which is called “runout”. That is, the fixed disc or rotor will not run absolutely truebecause you have manufacturing tolerances in its support includingbearings, hubs or axles, and in the disc itself, which is cast withangular portion therein. This rotating fixed rotor has a geometryenvelope within which its annular braking surface travels during a wheelrevolution. When a high spot on the rotor hits or rubs against a brakepad, it pushes against the high mass, caliper, and residual torque dragis the result. This reduces the life of brake pads and wastes fuel andenergy. Also, as the wheel is released by the ABS system to acceleratetoward the vehicle velocity, the wheel must overcome this residualtorque drag as it accelerates. This residual torque drag prolongs thetime needed to reach the desired wheel velocity and thus, increases thestopping distance for the ABS braking system. That is, the higherhydraulic operating pressures and mass of the sliding caliper andassociated friction losses of this sliding caliper system result in moretime betweens spin down and spin up. Hence, it would be desirable toprovide a more effective ABS system wherein the frequency of spin up andspin down is faster.

To provide an effective ABS braking system, the brake system itself mustpass rigorous specifications for wear, vibration, residual torque aswell as various road tests for brake fade, for temperature of operationon mountainous descents or curvy roads over long period of time, etc.Some of the current brake systems using two brake pads and a singlefixed brake disc operate at such high temperatures they either fail orare having difficulty in passing the Auto Motive Standard (AMS) roadtest.

Additionally, for a brake system to be installed on production vehicles,it must operate successfully and be free of vibrations, noise or otheradverse feel conditions that are deemed undesirable by the vehicleoperator. Of course, longevity of the brake pads and discs with aminimum of wear at localized areas that results in disc thicknessvariation (DTV) is most desirable to avoid vibrations and replacement ofbrake discs and/or brake pads. In an off-brake condition, the brake padsand brake disc can touch, particularly when cornering or traveling overbumpy surfaces and cause residual torque drag. This residual torque dragis additional to that above-described due to manufacturing tolerances.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a new andimproved ABS braking system for vehicles that is lighter in weight,lower in cost and has improved operating characteristics. To achievethese ends, the preferred ABS system is formed with a pair of slidable,thin brake discs, which are mounted in a floating manner on a wheel huband this floating allows the brake discs to position themselves quicklyand with reduced, residual brake torque. From a weight standpoint, thesebrake discs are thin, flat plates made of steel, aluminum or a compositematerial as contrasted to the heavy cast, angular rotors currently used.The hydraulic brake cylinder is integrally formed inside the stub axleor knuckle to provide a significant weight savings. From an operationalstandpoint, the ABS system works at substantially reduced hydraulicpressures and has a higher frequency of wheel deceleration andaccelerations, and lower amplitude of pressure and wheel velocities thanthat of the conventional ABS system. Thus, there is provided an ABSbraking system operating at a lower pressure, with reduced hystersis,and improved modulation of braking relative to a conventional,production ABS system which was a slidable caliper and a pair of brakepads cooperable with a single, fixed brake disc.

This is achieved by employing with the ABS electronic controller systemsa braking system using four rubbing or braking surfaces and two slidablediscs, a lighter and smaller caliper, greater caliper stiffness, reducedhystersis and lower operating forces.

In accordance with the invention, the preferred ABS braking system, whenused on a conventional vehicle having a standard ABS controller,develops from the initial application of the braking application aresolution of modulating scale for cycling that is associated with amuch lower coefficient of friction surfaces than is actually present.That is, the same ABS controller on a high coefficient of friction roadsurfaces operates the conventional, fixed, single brake disc system inthe manner associated with this high coefficient of friction surface butoperates the twin, slidable brake disc system in the manner associatedwith a much lower coefficient of friction, road surface. This is aresult of using the slidable pair of brake discs and four brake padsoperating at about one half of the usual hydraulic pressure and havingreduced residual torque drag and hystersis such that the initial cyclesused to scale or calibrate the modulators is one half or less than thatused for the conventional sliding caliper and fixed disc kind of system.Stated differently, when using a conventional ABS system controller andhydraulic master cylinder system connected to the preferred turn,slidable base discs and four brake pads, the system will provide morethan double the number of braking and release cycles per unit time. Thebraking and release cycles will have a much higher frequency and asubstantial less amplitude meaning that the vehicle will be deceleratingmore closely to the desired vehicle deceleration curve set by the ABScontroller.

In accordance with an important aspect of the invention, the slidablebrake pads are mounted upwardly at about a 12:00 o'clock position with awheel speed, pulse generator located adjacent thereto so as not tointerfere with the locking angle and turning circle of the vehiclesuspension. Preferably, the hydraulic cylinder is integrally formed atthe top of the suspension member. Also, it is preferred to provide theseal ring between the piston and the cylindrical wall of the cylinderwith a low friction surface, such as a Teflon surface, to reducehystersis.

In the preferred embodiment, the wheel speed pulse generator includes anannular air cooling ring attached to the rotatable hub with equallyspaced tabs arranged in a circle concentric with the wheel axle. Amagnetic sensor is mounted on the suspension member adjacent the fixedcaliper to sense the spaced tabs and thereby, the rotational speed ofthe wheel relative to lock-up and/or vehicle speed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagrammatic view of a twin braking ABS system embodyingthe invention;

FIG. 1B is a graph showing operational characteristics of the ABSbraking system of FIG. 1A applied to an automobile and embodying theinvention;

FIG. 1C is a graph showing operational characteristics of a conventionalABS braking system on the same vehicle used for FIG. 1A;

FIG. 1D illustrates a pressure reduction by about one-half and an aboutdoubling of frequency of brake application and release between the twinABS system of this invention and the conventional ABS system;

FIG. 1E illustrates a reservoir of hydraulic fluid mounted and hydrauliccontrol valve mounted on a vehicle wheel suspension and operable inaccordance with the invention;

FIG. 1F illustrates a solenoid force actuator mounted in a hollow boreof a stub axle of the suspension; and

FIG. 1G illustrates an ABS system for operating the preferred twin discbrake assembly;

FIG. 2 is a diagrammatic view of an outer spring constraining the brakepads and an inner spring constraining the brake discs;

FIG. 3 is a plan view showing the spring constraining the brake pads;

FIG. 3A is a cross-sectional view showing the spring applyingrestraining forces to the tops of the brake pad carriers;

FIG. 4 is a diagrammatic view of three leaf spring constraining a brakedisc on a hub;

FIG. 5 is an exploded view of the illustrative assembly;

FIG. 6 is a side elevational view of the illustrative assembly;

FIG. 7 is similar to FIG. 6 but shows the illustrative assembly invertical cross section;

FIG. 8 shows temperature decay curves for disc brakes due to residualdrag torque with the brakes off;

FIG. 9 shows curves for an AMS fade test of a standard fixed brake;

FIG. 10 shows the curves for an AMS fade test of a twin disc brake;

FIG. 11 is a vertical cross-sectional view taken through a suspensionlink of the illustrative assembly;

FIG. 12 is a view similar to FIG. 16, but of a modification of theillustrative assembly;

FIG. 13 is a perspective view of an alternative leaf spring havingraised ribs thereon;

FIG. 14 is a diagrammatic, enlarged view of the points of contactbetween the leaf springs and the brake disc;

FIG. 15 is an enlarged, fragmentary and exploded view of the drivingconnection between a hub and slidable brake disc;

FIG. 15A is similar to FIG. 15 except that the driving connection isenlarged and meshed to drive the brake disc with rotation of the hub;

FIG. 16 is a view taken in the direction of the arrow XVI in FIG. 6;

FIG. 17 is a view taken in the direction of the arrow XVII in FIG. 7;and

FIG. 18 is a view showing two solenoids to operate the brake padcarriers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in the drawings for purposes of illustration, the invention isembodied in an ABS braking system 9 (FIG. 1A) having an electroniccontrol unit 11 controlling a hydraulic system connected to a forceactuator 13 which supplies the actuating force used to operate a brakingdisc assembly 10 having a pair of brake discs 38 and 40 which are brakeddecelerated by clamping forces from four braking pads 50, 54, 56 and 60(FIG. 1G). The illustrated braking assembly will be described inconnection with the illustrated embodiment of the invention wherein thebraking system is for a front wheel (not shown) of a front wheel-drivecar. The ABS controlled braking system of this invention may be appliedto any vehicle whether front or rear wheel drive and to the rear wheelbrakes as well as the front wheel brakes.

The ABS braking system 9 of this invention employed the slidable pair ofbrake discs 38 and 40 and the cooperating four braking pads 50, 54, 56and 60 and employed a conventional ECU 11 provided on a productionautomobile. The braking system was tested on various combinations ofroad surfaces including, but not limited to, road surfaces with a verylow coefficient of friction, such as polished ice, as well as normal dryroad surfaces and combinations thereof. An ABS controller 15 develops atheoretical vehicle reference speed which is depicted herein as asubstantially linear deceleration curve 99 (FIGS. 1B and 1C) for thestopping distance depending upon a number of factors including thevehicle's velocity and the coefficient of friction for the surfaceengaging a wheel or wheels. Typically, each wheel is separatelycontrolled as one or the other of the wheels made by a lower efficientsurface such as ice while another wheel may be on dry pavement with ahigh coefficient of friction. In the example illustrated in FIG. 1B forthe twin braking disc assembly of this invention, the vehicle wastraveling at 80 kilometers per hour and then the brakes were appliedvery hard. The vehicle's wheel speed is sensed during the decelerationof the vehicle and is depicted in FIGS. 1B and 1C, as anacceleration/deceleration curve 100. This wheel speedacceleration/deceleration curve 100 has alternating wheel decelerationportions 100 a and wheel acceleration portions 100 b. Thus, will be seenfrom curves 100 on FIGS. 1B and 1C that the ABS control system appliesbrake shoes against the brake discs and releases the braking forceiteratively to decelerate the wheel and then to release the brakes toallow the wheel to accelerate towards the vehicle velocity. Herein, thecurve 100 is substantively linear from an upper left end 99 a where thevehicle is traveling at 80 kph until it is stopped at a lower right endportion 99 b on the curve 99. The horizontal axis of the graph is intime based units that can be with the vehicle having been stopped afterso many units of travel time.

Thus, the wheel acceleration/deceleration curves 100 each show the wheelbeing decelerated along the downward sloping portion 100 a when thebrakes are applied and an ascending portion 100 b, as the wheel brakesare released and the wheel is allowed to acceleration toward the vehiclevelocity, which is slightly less than the vehicle reference speed, asshown by the curve 99 immediately thereabove. A brake apply and releasecycle generates a deceleration beginning at a higher wheel velocity 100a and continuing to the lowest wheel 100 d and then the curve shows thewheel velocity rising along curve portion 100 b to another maximum wheelvelocity 100 c to initiate the brake apply and release cycle.

The graph of FIG. 1C was generated during the braking of a productionvehicle employing the single fixed disc or rotor and a slidable caliper(not shown) having a pair of brake discs. Similar reference charactershave been used on the curves of FIGS. 1B and 1C to designate the samethings such as deceleration, acceleration, vehicle velocity, pressure ofhydraulic fluid and the time or distance traveled. The conventionalsliding caliper and single brake rotor on the test vehicle were replacedwith the braking assembly having the twin discs and four braking padsillustrated here. The same ABS controller system was used to operate theconventional braking system as well as the twin disc braking systemillustrated and described herein. The curves of FIGS. 1B and 1C weregenerated for a pair of front wheels on a low coefficient of frictionsurface, viz. polished ice. Other data were generated for high frictionsurfaces and a combination of low and high friction surfaces.

Brake fluid pressure curves 102 are also provided in FIGS. 1B and 1C toshow the hydraulic pressure during each brake apply and release cycle.The downwardly sloping portion 102 a shows a dropping fluid pressure asthe brakes are released and shows an ascending fluid pressure portion102 b as the brakes are applied. For each iterative brake apply andrelease cycle the fluid pressure descends as the wheel acceleratestoward vehicle speed and then the fluid pressure ascends as the wheel isdecelerated toward the wheel locking condition. An average fluid brakepressure line 104 is also shown in FIGS. 1B and 1C. The brake pressureis modulated as by a hydraulic modulating valve 17 (FIG. 1A). When thewheel deceleration exceeds the vehicle deceleration by a defined amountthe ECU 11 signals the pressure modulating valve to modulate and reducethe line pressure. When the wheel accelerates and at a defined point,the ECU 11 signals the modulating valve 17 to restore line pressure.

In accordance with the present invention, there is provided an ABSbraking system having a finer resolution or frequency of brakes applyand release cycles and with the cycles being of less amplitude for wheelacceleration/deceleration. Additionally, the present invention providesa reduction in fluid pressure by about one-half, as can be seen from acomparison of the average fluid pressure curves 103 of FIGS. 1B, 1C and1D, which is desirable from a hystersis standpoint where the expansionand contraction of seals and expandable fluid hoses takes time andenergy. While the same amount of energy is needed to stop the vehicle,more energy and time is wasted due to hystersis. In addition to asubstantial reduction in pressure, it can be seen from a comparison ofthe respective pressure cycles, as depicted in FIG. 1D, that theamplitude of pressure changes is substantially smaller for the ABS twinbrake system than for the amplitude of pressure changes for theconventional braking system. Additionally, the fluid pressure cycles aremore frequent for the twin brake ABS system than for the conventionalABS system, as depicted in FIG. 1D.

As will be explained in greater detail hereinafter, in the twin brakeABS system, the wheel accelerates faster towards vehicle speed duringwheel spin-up portion 100 b because of a significantly less residualtorque drag from the twin disc and four brake system 10 as compared tothe conventional single, fixed rotor and slidable caliper. This residualbrake drag is present during the wheel spin-up while the brake is in therelease mode to retard the wheel acceleration.

From weight and cost standpoints, it is preferred to provide an integralhydraulic cylinder 72 (FIG. 5) formed in the stub axle 12 with a piston14 therein; thin slidable flat brake discs 38 and 40 of steel; and asmaller fixed caliper carrying the brake pads 50, 54, 56 and 60.Significant weight reductions for example from about 18 kilograms to 15kilograms has been achieved in this example. Further cost and weightsavings are achievable by using lighter weight and/or smaller seals andhoses because the reduction of about 50% in the operating pressurebetween the two ABS systems (FIGS. 2 and 3). A reduction of 3 kilogramsor more of unsprung weight at the wheels which transmit vibrations,noise and harshness back into the vehicle is an important andsignificant contribution. Thus, it will be seen that the presentinvention provides an ABS system which is lower in cost, lighter inweight, and operates more efficiently than the conventional ABS systemto which it is being compared herein. The present invention iscompatible with existing ABS control systems using existing algorithmsfor the conventional caliper system. Improved braking can be obtainedwith use of a new algorithm that utilizes the higher frequency and loweramplitude more efficiently than the algorithm developed for thisconventional, higher pressure, ABS controller. The finer resolution in asense reduces the “hunting” of the pressures about a center line oraverage line for the pressure changes shown in these graphs. Because ofthe finer resolution, it also may be desirable to increase the samplingrate, for example, by doubling the number of input elements around thewheel that are being sensed by a sensor, such as a Hall effect type ofsensor 11 a (FIGS. 1A and FIG. lG) to provide double the number of inputsignals to the ECU. Further, the input signals may be further magnified,and the flat bottom of a current signal may be processed to give a finerresolution of pressure variation at the changeover from a decreasingpressure to an increasing pressure at the brake pads. This additionalinformation could be of use in the new algorithm.

In accordance with an important aspect of the invention, the reductionin pressure being used to generate the braking clamping force over fourclamping surfaces rather than two clamping forces allows the use of asolenoid 110 (FIG. 1F) to operate the brakes rather than theconventional rotary electrical motors with gear trains to provide amechanical advantage. That is, as illustrated in FIGS. 1F and 18, asolenoid 110 or a pair of solenoids 110 and 112 may be used to providethe force for actuating the brakes at a force equivalent to 20 Bar orabout 10 Bar if a pair of hydraulic cylinders are provided in the stubaxles, as illustrated in FIG. 18.

From the date developed with the test vehicle, there was found to be areduction in pressure from about 70 BAR to 35-40 BAR for highcoefficient road surfaces. On low coefficient of friction road surfaces,such as ice, the conventional caliper system operated in a range of15-20 BAR of line pressure while the twin brake system operated at 6-10BAR of line pressure. The frequency was about double in each instance,and the amplitude of pressure variation was about halved. This is withthe use of a single cylinder 72 rather than a pair of cylinders, whichshould allow a further reduction by about one-half, if such a lowerpressure system is desired. These lower pressures are most useful forbrake-by-wire systems because this allows the use of the lower force,solenoids rather than the large force, complex, rotary motors and geartrains now used to provide a mechanical advantage in order to developthe high forces currently needed for the conventional caliper disc brakesystem.

The illustrated twin brake system shown in FIG. 1G will now be describedin detail and it comprises at least one pair of brake discs 38, 40 whichare mounted on a hub 14 of a suspension for a vehicle with the brakingdisc being constrained i.e., positioned on the hub 14, along its innerradial portion by a resilient radially directed force applicator 44acting between the hub 14 and the brake disc and by an outer forceapplicator assembly 45 which is positioned at the outer rim of the disc.This construction provides a rotational geometry for the disc to havecontact between the disc and the brake pads in a random nature, therebyresulting in a lower residual, off-brake torque and reduction of DTV.That is, a gentle random touching of the brake pads and brake disc mayoccur when driving straight ahead with the pads and disc being held innon-tilting positions relative to one another. The inner, radiallydirected, force applicator is positioned between the slidable disc, andthe hub to provide friction forces to the hub and to the disc whichholds them against sliding relative to one another and againstgenerating a noise or a high squeal when the brake disc is heated andexpanded. That is, when the brake disc was cold, no squeal or noise wasgenerated at the spline interconnection. But, when the disc was heatedand expanded, disc spline members or teeth 42 (FIG. 5) were loose andslid in hub splines 20 and generated high pitched squealing noises.

The preferred radial, inner force applicator 44 comprises springs,preferably flat leaf springs 44 a, that are laid tangentially of the hubat their centers 44 b (FIGS. 4 and 5) and with their outer ends 44 cbiased into contact with inner hub surfaces at spaced points, asillustrated in exaggerated form in FIG. 4. More spaced points of contactcan be provided by providing raised ribs 44 d on the leaf springs 44 x,as illustrated in FIGS. 13 and 14.

The slidable brake disc 38 is thus supported in a floating manner onpoints of contact 44 c (FIG. 4) with the leaf springs 44 a on the hub ina floating manner and the brake disc can be shifted axially with forcesapplied thereto to overcome the frictional forces being applied by thesprings at inner disc hub surface. When the brake disc expandsconsiderably due to a disc high temperature, the disc teeth become loosein the colder spline hubs and the frictional forces between the leafsprings 44 a and the brake disc and hub restrain the disc from shiftingrelative to the hub and a resultant squealing noise. The leaf springs 44a impart radially directed forces to the inner hub portion of the brakedisc to keep it generally in a plane normal to its rotational axisthrough the center of the hub. This inner radial positioning by thesprings 44 a assists in keeping the disc 38 concentric with therotational axis and within a relatively tight space envelope at thebrakes off condition thereby reducing rubbing contact between the brakepad's frictional surfaces and the brake discs 38, 40 and a resultantdisc thickness variation (DTV). DTV which is a major source ofvibration.

In accordance with an important aspect of the invention, slidable brakediscs 38 and 40 float on the hub 14 and its outer rim portion isconstrained to its off-brake position, and each disc seeks or floats toan off-brake position established by engagement with slidable brake pads50, 54 and 56, which slide on the guide surfaces 68 of the bridge-shapedguide member 64. As best seen in FIGS. 2, 3 and 3A, a brake pad, forceapplicator 71 is positioned to apply radially directed loads to theslidable brake pads to constrain them from sliding with predeterminedspring forces. The spring forces are much stronger than that neededmerely to prevent rattling or noise suppression. The spring forces aresufficient to restrain the slidable brake pads from moving into contactwith the brake discs in an uncontrolled manner. It has been found thatif only a light spring force is supplied to suppress noise, that thenoise will be abated; but that the brake pads are free to shift and rubagainst the brake discs causing wear and DTV. Also, when using verylight springs, the brake pads will not assist in positioning the outerrims of the slidable brake discs to reduce off-brake residual torque.The illustrated force applicator 71 comprises a pair of leaf springs 71a and 71 b (FIGS. 2 and 5) which form the dual functions of preventingrattle and positioning of the pads and discs relative to each other.

After the brake has been applied and released, the rotating brake disc38 initially rubs against the brake pads and forces from this rubbingcause the disc pads 50 and 56 to slide in opposite directions from therotating disc. The amount of shifting is controlled by the brake forceapplicator's frictional force being overcome. Conversely, the off-brake,residual torque position of the rotating brake disc 38 is beingconstrained by the forced-apart brake pads, which are being held againstfurther sliding by the force applicators. The force applicator springs44 also are controlling any lateral sliding of the brake disc 38 alongthe hub. The brake disc 38 is being constrained in its off-load positionby the outer force applicators acting on opposite sides of the pair ofdiscs and the inner springs 44 acting on the inner hub portion of thediscs. Thus, the disc is controlled to be free to slide and float butnot to topple into the brake pads and the brake pads have controlledsliding but are not free to topple or to be free to vibrate into or bangagainst the discs.

The ABS twin disc brake assembly 10 of the present invention, because ofits floating geometry as described above, has a significantly lower dragtorque, i.e., off-brake residual torque, as will be explained inconnection with FIG. 8 which illustrates a typical result for the disctemperature curves from 100 Kph. for the ABS twin disc brake versus aconventional, ABS disc brake. The conventional fixed brake curves 13Aplateaus at best is 350° C. above ambient while the ABS twin disc brake10 continues to cool and stabilizes at 10° above ambient, as illustratedby the straight line 13B. Usually, the conventional brake was found tobe about 50°-70° C. above ambient. The assumption made with respect tothis test is that dynamic drag due to disc face contact with the pad isproportional to temperature at the disc. The present invention isdesigned to preferably produce a low residual torque, e.g., about 1newton meter or less in contrast to about 6 newton meter for the fixeddisc brake on the vehicle being tested herein.

As explained above, the vehicle wheel being used in this ABS twin brakesystem can accelerate faster toward the vehicle speed because of lowerresidual torque drag than can the conventional ABS wheels having thehigh torque drag from the conventional disc brake.

In accordance with the invention, the brake discs 38 and 40 must be flatand planar in their rotational plane and substantially normal to therotational axis 9 (FIG. 2). The brake disc pads have outer planarsurfaces 50 a, 54 a; 56 a and 60 a which are held by the springs 71 aand 71 b to be parallel to the disc annular braking surfaces 38 a and 40a at the outer rim portion of the brake discs 38 and 40. When the discgeometry is slightly curved, i.e., not a flat planar surface, it hasbeen found that localized rubbing and wear occurred, as illustrated inFIG. 2, at a lower corner 50 b of the cylinder brake pads 50 and at theupper outer corner 54 b of the opposed brake pad 54 on the slidable padcarrier 58. FIG. 2 shows a very exaggerated tilted disc 38 in lines toillustrate the point being made. The non-flat brake disc did not haverandom contact with the brake discs 38 and 40; but had localized rubbingcontact due to the disc curvature at the inner and outer corners 50 band 54 b during each or almost each revolution of the brake disc. Severedisc thickness variations resulted and vibrations of the brake occurred.When the non-flat discs were replaced with flat brake discs the randomengagement of the pads and discs was again achieved, the DTV andvibrations associated with the DTV were eliminated. If a localized spotcarries the load, you get wear and a pumping action at wheel frequency.

While not illustrated herein, it was found that if the slidable brakepad surfaces 50 a, 54 a, and 56 a (FIG. 2) were not held in parallelrelationship to the brake disc faces 38 a and 40 a, but were freelymounted or loosely mounted on the bridge, that the brake pads could tiltor cock and cause DTV and resultant vibration, as described above for anon-flat brake disc. Stated differently, the springs 71 a and 71 b werestrong enough to hold the brake pads against a tilting that would shifttheir planar pad surfaces 50 a, 54 a and 56 a from planes perpendicularto the rotational axis 9 and would bring a corner thereof intocontinual, localized rubbing contact with a brake disc in the off-brakeposition. Thus, the floating geometry for the brake discs and constraintof the brake pads and discs to achieve random contact at the off-brakeposition is an important aspect of the invention.

AMS fade tests were run to compare the performance of the ABS twin discbrake assembly 10 of this invention versus the standard factory equippedfixed brake disc, and the results are shown in FIGS. 9 and 10. As seenin FIG. 9, there are ten peaks on the graph for each of the ten brakingstops with the brakes cooling and showing a temperature drop of about30° C. and a maximum disc temperature of about 700° C. which is theJudder range. In contrast, the ABS twin slidable brake disc system had amaximum temperature of 580° C. (FIG. 10) or about 120° C. lower than theconventional disc brake. The temperature drop between braking events wasabout 80° compared to only a 30° C. temperature drop for conventionaldisc brake. Thus, the present ABS system passed the AMS fade test wherethe conventional ABS brake system being tested did not pass the AMStest.

In accordance with the present invention, the preferred drive connection19 has the brake disc teeth 42 sized to fit the grooves 20 along both ofthe groove flanks 21 without using oversized grooves. This is incontrast to the prior art which used oversized spline grooves and smallsprings therein to engage the driving side flanks of the hub and disc;but this prior art solution led to other problems like disc wobble onthe hub. Preferably, the driving connection of the present invention isa very efficient one such as that akin to a pair of meshed gears wherethe contact is a line of contact across the engaged flanks 21 (FIG. 15A)rather than a small point of contact to provide lower unit pressures.Preferably, this line of contact is maintained whether the brake dischas a high or low temperature. The plastic deformation at the engagedspline surfaces keeps the engaged spline members clean from corrosion.The present invention eliminates the brinneling, dust generation, andsquirming of the disc at high braking torque.

The hub 14 is an integral casting and, as is conventional, has a hollowcylindrical rearward projection 14 a which has a splined interior, andan exterior, which provides a mounting for roller bearings 16 (FIG. 7).A splined projection of a constant velocity joint (not shown) at the endof a drive shaft is received within the projection so that the hub canbe rotated on the bearings 16 by the drive shaft. The hub also has anannular disc-like portion 14 b from which the portion projectsrearwardly. The hub provides a mounting for the wheel (not shown) whichis bolted against a forward surface of the portion by bolts received inholes 14 d. The hub also has a hollow cylindrical rearward projection 14c of greater diameter than the portion. The portion projects from theouter edge of the portion 14 b. The portion 14 c has an outer surfaceprovided with grooves 20 running parallel to the axis 22 about which thehub rotates. The grooves 20 are arranged in four equallycircumferentially-spaced locations.

The suspension link 12 (FIG. 11) is an integral casting and comprises ahollow cylindrical portion 12 a of conventional form, which provides amounting for the bearings 16 so that the hub 14 rotates on the link. Thelink also comprises top 24 and bottom 26 mountings for supports of thelink. The top mounting is provided by a portion 12 b of the link whichprojects rearwardly from a portion 12 c which projects upwardly from theportion 12 a. The portion 12 b is of conventional form and forms twosemi-cylindrical arms (FIG. 5) which together form a clamp which can betightened by a bolt (not shown) which extends through bores 28 in thearms and across a gap between them. A McPherson strut (not shown) can beclamped between the arms of the portion 12 b so that the link can pivotabout the longitudinal axis of the strut.

The bottom mounting 26 is provided by a portion 12 d of the link 12,which projects downwardly from the portion 12 a thereof. This portion 12d is of conventional form and has a vertical bore 30, to receive a pinof a ball joint (not shown), and two horizontal bores 32 in which bolts(not shown) can be received to connect the link to a tie bar (notshown).

The link 12 also comprises an arm 34 for connection to a track rod (notshown) of a steering system of the vehicle. This arm 34 is ofconventional form and is provided by a portion 12 e of the link 12,which projects sideways from the portion 12 a thereof. The arm 34comprises a vertical bore 36 through which the arm can be pivotallyconnected to the track rod. In order to steer the vehicle, the track rodis moved to cause the link to pivot on the joint 18 and the mountings 24and 26.

The twin discs 38 and 40 are identical to one another and are mountedfor limited movement on the hub 14 in a direction generally parallel tothe axis 22 about which the hub rotates. Specifically, each disc is inthe form of a flat annular plate and has inwardly-projecting teeth 42.As best seen in FIGS. 5, 15 and 15A, it is preferred that the brakediscs 38 and 40 each have a limited number of wide teeth, i.e., theillustrated four teeth 42 that mesh with the spline grooves 20 a ofsplines 20 on the hub. The spline grooves 20 a are four in number, inthis instance, and have flanking walls 21 (FIG. 15) that match flankingwalls 42 a on brake disc teeth 42. The engaged flanks 21 and 42 a havean angle A for their respective tooth flange angles. Manifestly, thenumber of teeth and splines may be varied. Because of large stressesgenerated on the thin teeth 42 on these relatively thin brake discs,there is a tendency of stress cracks to form, particularly after hightemperature heating and cooling cycles and high stress cycles. Torelieve such stress, there are provided large, curved, stress relieffillets or cut-outs 42 b in the respective brake discs. Herein, as shownin FIGS. 15 and 15A, the stress relieving fillets are provided on eachside of a tooth 42 and provide generally semi-cylindrical,cross-sectional openings on each side of each tooth, when the teeth arefitted into a spline grooves, as shown in FIG. 15A.

As best seen in FIG. 5, the four grooves 20 on the hub are relativelysmall compared to the projecting teeth 20 b defined between each pair ofadjacent grooves 20. These teeth 20 b on the hub have large, arcuatesurfaces 20 c against which are laid the leaf springs 44. Thus, eachleaf spring 44 has a large circumferential area contact with inner,arcuate surfaces 42 c of the brake disc in the place between dependingteeth 42 thereon.

Four leaf springs 44 are mounted on the hub 14 to provide resilientforce applying means to apply radial forces between the hub and thediscs 38 and 40. These radial forces prevent the discs from tilting onthe hub, prevent rattling and control sliding of the discs along thehub. The resilience of the springs allows thermal expansion to beaccommodated, as explained above. The springs are secured in a suitablemanner, such as by screws 46 to the outer surface 20 c of the hubportion 14 c in the gaps between the spline grooves 20 a. Each of thefour springs engages both of the discs 38 and 40 in the areas betweenthe teeth 42, giving a resilient four-point mounting for each disc. Thediscs can slide on the hub parallel to the axis 22 with the teethsliding in the spline grooves 20 a.

As best seen in FIG. 4, the flat leaf spring 44 is engaged with and hasa pressure line of contact with the hub at point 44 b; and the outerends of the spring 44 c have been flexed downwardly to provide pressureline of contact engagement with the discs 38 and 40 at these bent springends. In order to provide more lines of engagement between the disc andthe hub, the spring 44 x may be provided with ribs 44 d therein, asshown in FIGS. 13 and 14. Also, it is preferred to separate the spring44 into separate biasing portions 44 h and 44 i (FIG. 13) separated by aslot 44 j each portion acting on an associated disc 38 or 40 to providemore individualized, independent pressure forces between the associateddisc and the hub. The springs 44 are balanced in the force they apply tothe brake discs 38 and 40 relative to the force which the springs 71 aand 71 b apply to the slidable brake pad carriers 52 and 58. Both thebrake discs and the brake carriers are constrained against shiftingalong the hub and the bridge respectively, due to vibrations andinertial forces from the vehicle when it is traveling. Thus, it will beseen that the springs 44 allow the slidable brake discs to: float on thehub, hold the discs in a radial plane normal to the rotational axis,apply frictional forces that prevent squealing; apply frictional forcesthat aid in holding the discs in position while rotating in theiroff-brake positions; and permit axial forces from the force actuator tooutwardly slide the discs to their braking position with engagement ofthe disc 40 with the stationary brake pad 60.

Turning now in greater detail to the illustrated brake pads, these padscomprise the first pad 50 which is mounted on a backing plate 52 and isarranged to engage a side surface of the disc 38, pads 54 and 56, whichare mounted on opposite sides of a backing plate 58 and are arranged,respectively, to engage the opposite side surface of the disc 38 and afacing side surface of the disc 40, and the pad 60 which is mounted on abacking plate 62 and is arranged to engage the opposite side surface ofthe disc 40. The backing plate is fixedly mounted on a guide member orbridge 64, which is, in turn, fixedly mounted on the portion 12 c of thelink 12. Specifically, two bolts 66 pass through bores through theportion 12 c and the guide member 64, and have threaded ends which arereceived in threaded bores in the backing plate. The stationary guidemember 64 provides two guidance surfaces 68 on which the backing plates52 and 58 slide. The guidance surfaces 68 extend, parallel to the axis22, along opposite sides of the member 64. The guidance surfaces maytake other forms such as the shafts of the bolts 66.

Each guidance surface 68 receives a pair of concave, U-shaped projectionor hooks of the pad carriers 52 and 58. As best seen in FIG. 3A, theslidable pad carrier 58 has hook-shaped projections 59 with innersliding surfaces 59 a, which are slidably supported on theupwardly-facing support surfaces 68 of the bridge 64. To assist inachieving the desired balance to allow the brake pad carriers 52 and 58to be pushed apart from and by the brake discs 38 and 40, when they areshifting axially from their brakes-on to their brakes-off positions; andyet constrain the pad carriers and their brake pads from tilting, it ispreferred to machine flat the inner sliding surfaces 59 a on thecarriers and the supporting surfaces 68 on the bridge. Flat machinedsurfaces on the carriers engaging flat machine surfaces on the bridgeassures a more uniform, frictional, constraining force to retain thebrake pad carriers against axial sliding from their off-brake positions.Also, the carriers will have broader, wider engagement with bridgesupporting surfaces 68 to assist in preventing significant rocking ortilting on the bridge under vehicle inertial forces and/or vibrationswhen the vehicle is moving, as would cause localized rubbing contact inthe off-brake condition.

If the slidable brake pad position is not controlled, the slidable brakepad may tilt to engage or to vibrate against the slidable brake disc andgenerate a random wear pattern on the disc causing DTV and vibration ofthe disc. The control of the slidable pad and disc is important in avery dynamic situation with the vehicle wheel carrying the slidablebrake system over bumpy or smooth roads, cornering with brakes on,cornering with brakes off, with ABS system on, with an ABS system off,etc. On cornering, the hub deflects and moves the disc surface to engagethe brake pad; and after cornering, the pad and disc separate as thebrake recovers to its steady state of low residual torque at theoff-brake position. In the embodiment of the invention, illustrated inFIGS. 2, 3 and 3A, the preferred force applicators comprise flat leafsprings 71 a and 71 b that have been bent from their flat planarcondition to a bow configuration in which outer edges 71 c and 71 d ofthe springs abut top end surfaces 52 a, 52 b, 58 a, 58 b of therespective slidable brake carriers 52 and 58. The center portion of theleaf spring 71 a is secured by a suitable fastener, such as screws 69threaded through the spring and into the stationary bridge 64 at acentral location on the top of the stationary bridge 64.

The force applicator 71 may take many forms, and it is hereinillustrated in FIG. 3 as having the two separate leaf spring portions 71a and 71 b, each of which is separately applied resilient, biasingforces to its associated brake pad holder 52 or 58. The leaf springportions 71 a and 71 b are preferably connected by a short integral,central web 71 f, which is located between a pair of facing, elongatedslots 77 dividing the spring leaf into the two discrete spring forceapplicator sections. Thus, if one brake pad holder has high pointsthereon or other force mitigating or amplifying factors affecting it andits associated spring; the other brake pad holder and its associatedspring should be isolated therefrom.

As previously explained in the embodiment of FIGS. 1-17, the brakeactuating force used to brake the vehicle is from a brake actuator whichis in the form of a hydraulic piston and cylinder assembly 75. In theembodiment of the invention described in connection with FIG. 18, as analternative to the use of an electric motor and a gear drive used in theprior art, brake-by-wire ABS systems, the solenoid 110 (FIG. 1F) or pairof solenoids 110 and 112 (FIG. 18) may shift the movable brake padcarriers 52 and 58 to carry the slidable brake pads into theirrespective braking positions and slide the brake discs axially along thehub 14 into their respective braking positions.

The illustrative force actuator system comprises a piston and cylinderassembly operable to urge the pads 50, 54, 56 and 60 into engagementwith opposite side surfaces of the discs 38 and 40 to brake the hub 14and hence, the wheel. The piston and cylinder assembly comprises acylinder 72 which is defined by the portion 12 c of the link 12. Thus,the cylinder is formed integrally with the remainder of the link. Abrake-by-wire actuator such as the solenoid 110 shown in FIG. 1F or anelectric motor (not shown) may be mounted in the hollow cylinder bore 72rather than the piston 74. Herein, the piston 74 of the assemblyprojects from the cylinder and engages the backing plate 52 on theopposite side thereof to the pad 50. The piston and cylinder assembly isoperated by supplying hydraulic fluid under pressure to a bore 76 in thelink portion 12 c which communicates with the cylinder. Herein, thehydraulic pressure for operating the twin disc brake system was about 30to 35 BAR which is one-half of the 70 BAR pressure of the conventionalfixed disc brake on the other test vehicle. The piston had a face ofabout 200 mm in area. The piston moves out of the cylinder moving thebacking plates 52 and 58 and the discs 38 and 40 until the disc 40engages the pad 60, which does not move.

The hydraulic piston and cylinder assembly 75 includes a seal which actsbetween the cylinder 72 and the piston 74 to prevent egress of hydraulicfluid from the cylinder. This seal is provided by an elastomeric sealingring, which is mounted in an annular groove formed in a cylinder wall,the ring projecting from the groove to engage the piston. This sealingring also serves as an energy storing mechanism. Specifically, when theassembly is operated to move the piston outwardly of the cylinder to putthe brake “on”, the ring is compressed thereby storing energy therein.When the pressure of the hydraulic fluid in the cylinder is reduced, thering releases the stored energy therein by moving the piston inwardly ofthe cylinder (away from the brake disc). Accordingly, the sealing ringhas to engage the piston with a significant force. Movement of thepiston away from the disc allows the movable pads 50, 54 and 56 of thebrake to be moved away from the disc by forces exerted thereon by therotating slidable brake discs 38 and 40 overcoming the force of thespring 71 a and 71 b; thereby putting the brake into a “brakes-off”condition.

The return of the piston 74 by the seal reduces the off-brake torquebecause there is no significant force being applied by the piston to thebrake carrier 52 and its brake shoe 50 relative to the facing side ofthe slidable brake disc 38. Conversely, the floating brake discs 38 and40 are constrained and float on the hub 14 and will not shift the pistoninwardly into the cylinder to displace hydraulic fluid, in the cylindercausing “knock-back” during cornering or other dynamic movements of thewheel assembly. The reduction of knock-back provides a better feel toapplying the brakes with less fluid displacement, and eliminates theoccasional long pedal displacement feel where substantial fall-back hasoccurred.

From the foregoing, it will be seen that the present invention providesa much smaller disc brake assembly without the very large calipersliding and bolts as in the conventional, fixed disc brake. The caliperis large because it carries the cylinder and piston and the slidablebridge must withstand and transfer the large torque brake loads. Thepresent invention is smaller because the cylinder can be integrated withthe support and the bridge does not slide and carry the piston. Becauseof knock back and other problems, this large fixed brake is usuallymounted at about 3:00 or 9:00 o'clock positions whereas in the presentinvention the brake is mounted at the top of the unit at the 12:00o'clock position. The stiffness problem of the bridge with itsdeflection, e.g., 0.006 inch, is reduced by a factor of four when usingfour brake pads and one-half the hydraulic line pressure allowing asmaller and lighter weight brake assembly. The time of mounting andassembly of the brake, as well as repair or replacement, is enhancedbecause of the front bolting and the telescopic sliding of the brakediscs and of the brake components versus the bolt from the rear orbehind of the fixed brake bolts on which the caliper slides.

As explained above, the ABS twin brake system of this invention operatesat about one-half of fluid pressure of the conventional ABS for the samevehicle. If it is desired to reduce the pressure again by aboutone-half, a pair of hydraulic cylinders 102 (FIG. 12) may be used ratherthan a single cylinder within the stub axle. Alternatively, a pair ofsolenoids 110 and/or 110, 112 (FIG. 18) could be housed in bores in thestub axle rather than a single solenoid to reduce the force needed andto supply redundancy of operation if one solenoid should fail. The brakecylinder of FIG. 16 and the pair of brake cylinders of FIG. 12 for theactuator system 100 of FIG. 12 have like parts which are given the samereference numerals and are not further described. The assembly 100 hastwo parallel cylinders 102 formed in portion 12 c of the stub axle. Inthis case, each of the cylinders 102 has a smaller transversecross-sectional area than the cylinder 72, but the total area of thecylinders 102 is greater. Each of the cylinders 102 has a piston 104therein and the pistons 104 cooperate in pressing the backing plate 52.In order to accommodate the two piston and cylinder assemblies, theguide member 64 is modified to arch over the pistons, as shown at 106and the bolts 66 are replaced by three bolts 108. The use of two pistonand cylinder assemblies enables greater force to be applied for the samepressure in the cylinders (or the same force to be applied for lowerpressure) and this force can, on average, be applied at a greaterdistance from the axis 22. If desired, the two cylinders can be ofdifferent diameters, e.g., with the leading cylinder in the normaldirection of rotation, being of greater diameter.

In the illustrated embodiment of the invention described herein, theforce actuator for the applying of the brake clamping pressure has beenfrom the conventional vehicles hydraulic system having a common mastercylinder and hydraulic lines or hoses extending from the master cylinderto four cylinders, such as the illustrated two, front wheel cylinders,the rear wheel cylinders for operating the rear drum brakes, have notbeen illustrated herein.

In accordance with a further embodiment of the invention illustrated inFIG. 1E, a master cylinder 13 a (FIG. 1A) and its lines 13 b have beeneliminated and each stub axle of the suspension, or another part of thesuspension, is provided with its own localized caliper unit having itslocalized hydraulics. More specifically, the stub axle or suspension 200is provided with a small reservoir or hollow portion 202 in a stub axlewith a fluid connection, such as a bore hole 204 in the stub axleleading to the hydraulic cylinder 72 to operate the piston to slide theslidable brake pads 50, 54 and 56 to force the outer brake disc intoclamping engagement with the outer, fixed brake pad, as described above.

To maintain the desired hydraulic pressure in the small cylinder 200 onthe suspension 200, a pressure generator device 206 (FIG. 1E) is mountedon and attached to the reservoir, and the energy used to increase thehydraulic pressure in the reservoir is derived from the mass of thevehicle as it bounces up and down. More specifically, the dampeningsystem for the vehicle wheel including shock absorbers or the like areused to actuate a pressure generator device. For instance, a plunger 210is mounted to be pushed by the vehicle mass to move a diaphragm 212 inthe reservoir 202 to increase the pressure to the desired constantpressure, e.g., 20 BAR. Currently, there are air rides or cushions invehicles that use the mass of the vehicle to increase air pressure inthese kinds of dampening systems and similar devices may be used as apressure generator for the hydraulic fluid in the reservoir 202.

To provide the ABS control for the ABS Braking System 200 preferablyincludes its own ABS controller, such as in the form of a computer chip214 or the like, mounted on the stub axle along with a pressure controlor modulating valve unit 215. Additionally, a small control valve 216for the ABS controller is provided on the suspension of each wheel tocontrol the hydraulic pressure and actuation of the piston in thecylinder 72 to decelerate the wheel and to release hydraulic pressure toallow the wheel to accelerate toward the vehicle velocity. Thepreferred, hydraulic, control valve unit 215 has a modulating valveincluding a plunger 217 operating in a fluid filled chamber 218 and bysliding the plunger forwardly to reduce the volume in the chamber 218the pressure is increased in the cylinder 72. Conversely, by pulling theplunger 217 rearwardly the volume in the chamber is increased and thehydraulic pressure in the brake cylinder 72 is reduced. The plunger 217is shifted either in predetermined increments of travel or in infinitetravel amounts by a solenoid 220 having a solenoid rod 221 forreciprocating in the solenoid case. The solenoid rod 221 has one endattached to the plunger. The solenoid is operated by the ABS controller214. In contrast to the conventional system having a modulating valve 17(FIG. 1), the modulating valve 215 sees a positive pressure from thereservoir rather than stopping fluid inflow through a check valveconnected to the master cylinder.

What is claimed is:
 1. A vehicle wheel brake system for a wheel suspension assembly and having an anti-lock braking system (“ABS”) to provide a higher resolution brake apply and brake release relative to an ABS system having a single, fixed brake disc, the brake system comprising: a mounting hub for a road wheel mounted on the wheel suspension assembly for rotation about a rotational axis; at least two slidable brake discs mounted to slide axially along the hub between braking and off-brake positions; a caliper including a fixed bridge and at least four (4) braking pads mounted on the fixed bridge to provide four braking surfaces for braking engagement with the opposing sides of each of the brake discs; a pulse creator mounted on the hub for generating pulses; a sensor mounted on the wheel suspension assembly for sensing pulses from the pulse creator and for providing signals with respect to the rotational condition of the road wheel; an ABS controller connected to the sensor and providing signals when the wheel condition is within preset parameters relative to the speed of the vehicle to develop a theoretical deceleration curve for the stopping of the vehicle within a predetermined distance; and a brake actuator system operable manually by the vehicle passenger and operable automatically by the ABS controller to operate the caliper to slide the brake discs axially and to cause application of the four brake pads at a pressure of about one-half or less of the pressure of operation of the fixed, brake disc system and a frequency of brake apply and release of at least double the frequency of brake apply and release of the fixed, brake disc system.
 2. A vehicle wheel system in accordance with claim 1 wherein a hollow bore is formed in the suspension member to reduce the weight of the suspension member and to contain the force applicator at a location closer to a wheel-turning axis to allow a reduction in turning radius.
 3. A vehicle wheel ABS braking system in accordance with claim 1, having reduced residual torque drag, comprising: springs between the hub and inner portions of the slidable brake discs to mount the brake discs in a floating manner on the hubs; and springs on the fixed caliper for holding the brake pads in position relative to the brake pads during vehicle wheel speed-up.
 4. A vehicle wheel ABS braking system in accordance with claim 1 having reduced weight and reduced residual drag torque, comprising: a hollow, cylindrical bore formed in the suspension member having a force actuator contained therein; springs floating and supporting the slidable brake discs on the hub; and springs on the caliper for engaging the slidable brake pads and for holding them in position relative to the slidable brake discs in the off-brake position to reduce residual torque drag therebetween.
 5. A vehicle wheel braking system, in accordance with claim 1, wherein the brake actuator system comprises: an integral, hydraulic cylinder for holding a hydraulic fluid integrally formed in a suspension member of the wheel suspension; and a piston mounted in the integral hydraulic cylinder and is operable by the hydraulic system to engage the four brake pads with the two axially, slidable brake discs.
 6. A vehicle wheel ABS braking system, in accordance with claim 1, wherein the brake pad actuator comprises a solenoid and an electrical system for selectively energizing and de-energizing the solenoid.
 7. A vehicle wheel ABS braking system, in accordance with claim 1, wherein the brake actuator comprises: a hydraulic system having a hydraulic cylinder at each wheel; a hydraulic reservoir for containing hydraulic fluid at each of the ABS-controlled brake pads to supply hydraulic fluid to an adjacent, hydraulic cylinder; and a pressure generator at each wheel suspension operable by the mass of the vehicle for pressuring the hydraulic fluid in each hydraulic reservoir.
 8. A vehicle wheel ABS braking system, in accordance with claim 1, wherein the pulse generator comprises a ring of spaced generator elements mounted on a side of the rotatable hub; and the sensor comprises a magnetic sensor disposed on the suspension member closely adjacent the ring of spaced generator elements.
 9. A vehicle wheel ABS braking system, in accordance with claim 1, wherein the caliper is mounted on the suspension member in a vertical plane through the rotational axis and above the rotational axis and a radially outer position relative to the rotational axis; and the pulse generator and the sensor are located radially inwardly of the caliper.
 10. A vehicle disc brake and suspension system having an ABS system comprising: a wheel suspension member having a hub and connections to other portions of the vehicle steering device; at least two brake discs each having an inner portion slidably mounted on the hub for sliding in a direction parallel to the central axis of the hub between a braking position and off-brake position; at least four braking pads including one outer, fixed, brake pad and at least three slidable brake pads each having a friction pad surface for applying braking torque to opposite sides of the brake disc when in the braking torque position to decelerate the engaged brake discs; a hollow bore in the suspension member; an actuator in the hollow bore of the suspension member for sliding the slidable brake pads and brake discs into the braking position; force applicators for floating the brake discs to allow them to slide axially from a braking position to an off-braking position relative to the braking pads; an outer rim portion on the braking disc rotating while in the off-brake position and engaging the slidable brake pad's friction surface to slide the pad from the braking position to an off-brake pad position; a caliper fixed to the suspension member and having slidable brake pads thereon operable by the actuator into braking engagement with the slidable brake discs; a brake pad force applicator acting on the slidable brake pads, when its off-brake position, to constrain the friction pad surfaces engaging the brake disc to reduce tilting of the brake pads on the stationary support and its rubbing on the brake discs that would increase off-brake, residual torque; and an ABS system for operating the brake pad force applicator within the hollow bore in the suspension member to slide the brake pads and brake discs iteratively to the braking position and releasing the brake pads and discs to slide to off-brake positions.
 11. A vehicle ABS brake system, in accordance with claim 10, wherein the actuator for sliding the brake pads comprises a hydraulic cylinder and a piston in the cylinder for applying the brake pads at 40 BAR or less when the vehicle is on a high coefficient of friction road surface.
 12. A vehicle ABS system, in accordance with claim 10, wherein the actuator for sliding the brake pads comprises a solenoid and an electrical system to operate the solenoid.
 13. The vehicle ABS braking system, in accordance with claim 10, wherein the brake pad force applicator acts on the slidable brake pads, when the system is in an off-brake position to constrain the friction pad surfaces from engaging the brake discs and to reduce tilting of the brake pads and rubbing on the brake discs that increases off-brake, residual torque.
 14. A disc brake system, in accordance with claim 13, wherein the brake pad force applicator applies force to each slidable brake pad to hold its face in a plane substantially parallel to the plane in which the disc is rotating to minimize tilting of the brake pad into engagement with the brake discs, which would cause disc thickness variation.
 15. A disc brake system, in accordance with claim 14, wherein the brake pad force applicator comprises at least one spring pushing on the brake pads in a direction substantially normal to the rotational axis of the brake discs and normal to the path of travel of the brake pads along a stationary support.
 16. A disc brake system, in accordance with claim 10, wherein a stationary support comprises a bridge; the slidable brake pad comprises a slidable pad carrier mounted for sliding on the bridge and carrying the frictional pad surface thereon; and the brake pad force applicator is positioned over the brake pad carrier and forces the brake pad carrier downwardly against the bridge.
 17. A vehicle wheel suspension system having an ABS braking system comprising: a suspension member; at least one brake disc mounted on the suspension member for rotation with a wheel of the vehicle, brake pads mounted on the suspension member for movement to a brake application position to engage the at least one brake disc to decelerate the wheel and for movement to a brake release position to allow the wheel to accelerate during an ABS braking operation; a localized hydraulic system at each of a plurality of wheels without connection to a master cylinder for shifting the brake pads to the brake application position and for allowing the brake pads to shift to the brake release position; a hydraulic reservoir mounted on the suspension at each wheel for containing hydraulic fluid; a pressure generator at each wheel suspension independent of a connection to a master cylinder for an associated hydraulic reservoir operable by the vehicle mass movement to increase pressure in the reservoir; and an ABS control system including an electrically operated actuator at each wheel suspension for operating the localized hydraulic system at each wheel suspension to iteratively shift the brake pads into the brake application position with vehicle wheel acceleration with intervals therebetween of wheel acceleration to stop the vehicle.
 18. A vehicle suspension and ABS braking system, in accordance with claim 17, wherein the at least one brake disc comprises a pair of brake discs slidable mounted on the hub; and wherein four brake pads are mounted on the suspension member to engage four faces of the pair of brake discs.
 19. A vehicle suspension and ABS braking system, in accordance with claim 17, wherein the hydraulic system comprises: an integral, hollow cylinder formed in a stub axle suspension member; and a piston mounted in the integral, hollow cylinder.
 20. A vehicle suspension and ABS braking system, in accordance with claim 17, wherein the ABS control system comprises an intelligent control located at each wheel for controlling that wheels iterative brake application and brake release.
 21. A method of braking a vehicle wheel using an ABS system having an ABS hydraulic system and an ABS controller, and a wheel brake having a caliper and at least two of slidable brake discs axially slidable on a rotatable wheel supporting hub and having at least four brake pads engageable with the brake discs, the method comprising: operating the caliper to a braking position using 40 BAR or less of hydraulic fluid pressure to slide the brake pads and the slidable brake discs to a braking position; releasing the hydraulic fluid to allow the slidable brake discs to slide axially on the hub and to engage the slidable friction pads and to push them to their off-brake positions; floating the brake discs and the brake pads on their respective supports in the off-brake position to reduce off-brake frictional drag and tilting of this brake pads against the brake discs; sensing operation of a brake pedal by the operator generating an excessive braking force and sensing wheel speed and an approaching lock up of the road wheel using an ABS controller; activating the ABS hydraulic system by the ABS controller to shift the slidable brake pads on the fixed caliper with hydraulic pressure at 40 BAR or less; and shifting slidable brake pads and slidable brake discs on their floating supports rapidly to the braking position with changes in pressure from 40 BAR and at a predetermined frequency in accordance with a stored algorithm in the ABS system.
 22. A method of braking, in accordance with claim 21, including a reduction of weight of the system by forming a hollow, cylinder actuator bore in the suspension.
 23. A method of braking, in accordance with claim 21, including positioning the caliper at about a 12:00 o'clock position and above the rotating hub.
 24. A method, in accordance with claim 21, including operating the piston within an integral cylinder at the top of the suspension member.
 25. A method, in accordance with claim 21, including operating the caliper by the ABS controller in the ABS mode at 40 BAR or less pressure on a high, co-efficient of friction road surface and at a substantially higher frequency than a system operating at about 70 BAR or more pressure on the same high coefficient of friction road surface.
 26. A method, in accordance with claim 25, including the step of operating the brake pads to engage and release the brake discs within the range of 8-20 Hertz for a low, coefficient of friction road surface. 